代码编辑器：
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var_dump(checkdate(12,31,-400));3
echo "<br>";4
var_dump(checkdate(2,29,2003));5
echo "<br>";6
var_dump(checkdate(2,29,2004));7
var_dump(checkdate(12,31,-400));echo "<br>";var_dump(checkdate(2,29,2003));echo "<br>";var_dump(checkdate(2,29,2004));